I suspect this is not an uncommon situation among programmers.
So when you go to another project that made different decisions, what you should do is understand the decisions. It's quite easy. And that's why it's what people do do, and it's why people are capable of contributing to projects other than their first.
If you program in C++, it's the same skill you used to learn one or more of {CMake, Makefiles, scons, bash, python} except it's easier because you already understand the programming language's model.
"No true Scotsman" and all, please refrain from posting messages that add nothing of value besides petty insults thrown in broad brush strokes.
Picking up features in a language you already use is easier than learning the language to begin with which itself is easier than learning to program at all. If you were able to read the documentation to get to 50%, you have all the skills needed to pick up the rest and get to the difficult part of picking up a new project: understanding the problem space. If you're capable of learning the meaning of an API you've never seen before - and you will, if you're not writing your last project verbatim - then you're capable of learning what a lambda means. This is not me saying that all programmers should be able to do this, it's me saying that doing this is a predicate of engineering software.
You accused anyone who did not agreed with you of being incompetent and immature. In the very least own your own claims.
That makes as much sence as claiming that to develop software in, say, Python on the real world you have to learn and deal with all of its standard library.
That is not the case. That has never been the case ever for any programming language, be it large or small. Specially in C++, where since it's inception the standard approach is to, at best, adopt a subset of all features and stick with it.